1. Field of the Invention
The invention relates to a driving device for a motor such as a stepping motor, and so forth, for controlling an angle and a speed of the motor.
2. Description of the Related Art
Following enhancement in performance of equipment driven by a stepping motor, the stepping motor is required to be rotatable in a wider range with low vibration, however, since the stepping motor is rotated by changing over energizing conditions of respective motor windings every time a command pulse given from outside is impressed, there arise problems of occurrence of vibration and step out, accompanying changeover of the energizing conditions.
With the stepping motor described above, there has been generally adopted micro-step driving whereby exciting currents of the motor windings are caused to change smoothly by use of a PWM inverter of a pulse width modulation mode (PWM mode) as means for reducing vibration. That is, a micro-step function is provided by the PWM inverter whereby the motor windings are energized with motor winding currents varying in the form of a sine wave every time an external command pulse is impressed to subdivide a fundamental step angle, thereby rotating a rotor step by step every time the external command pulse is impressed.
With a conventional motor driving device for a two-phase stepping motor using the PWM inverter described above, by inputting an angle command θ*, an α-phase current command iα*, and a β-phase current command iβ*, there are found deviation between iα* sin θ* and an exciting current iαf of an α-phase motor winding, and deviation between iβ* cos θ* and an exciting current iβf of a β-phase motor winding, and voltages proportional to the deviations, respectively are impressed to the respective motor windings. Thus, in order to feed the exciting currents in accordance with the α-phase current command iα*, and the β-phase current command iβ*, respectively, the voltages impressed to the α-phase and β-phase motor windings are controlled by current control systems independent from each other.
In the case of such conventional techniques as described, since there exist a plurality of the current control systems independent from each other, there has been the need for installing the current control systems in the same number as the number of phases according as the phases of a stepping motor is increased, causing a problem of complexity in configuration.